1. Field of the Invention
The present invention relates to an electric vehicle provided with a propelling motor which is driven by a battery power source, and particularly to a drive for driving an electric vehicle and a method for controlling the same.
2. Description of Prior Art
As a next-generation alternative vehicle for internal combustion engine vehicles such as gasoline automobiles, an electric vehicle using a propelling motor is attracting attention these years. It is said that the electric vehicle which uses a clean electric energy can completely remedy the environmental problems such as harmful noises and exhaust gases, which are about 70% of the causes for the environmental pollution, derived from the internal combustion engine vehicles, and can extend by two times or more the resource life of fossil fuel such as petroleum.
The electric vehicle has propelling wheels suspended by a shock absorber from the vehicle body in the same way as a conventional gasoline automobile and is propelled by a power transmission device with a motor as the drive source. And, the motor has electric power supplied by an electric power supply.
This electric power unit comprises a battery power supply unit using a plurality of storage batteries, a power supply circuit for supplying stable electric power, a motor for propelling, a motor driving circuit for directly controlling the propelling power of the motor, and a control circuit for outputting an operation command or the like to the motor drive circuit. And, the motor-driven power from the motor is transmitted to the propelling wheels via a power transmission to drive the vehicle.
Such a power transmission is known to use the one which is used for a conventional gasoline automobile and a single propelling motor 52 is provided instead of an engine as shown in FIG. 13. A power transmission 51 of an electric vehicle 50 comprises a transmission 53 directly connected to the motor 52 which is provided at the front of the vehicle, a propeller shaft 54 which is connected to the transmission 53 to transmit the drive force backward, and a differential gear 57 for distributing the drive force to a rear axle 56 to which rear right and left wheels 55, 55 are connected. And, the motor power is lowered by the transmission 53 to drive the rear wheels 55, 55. It is also known to directly connect the motor 52 to the propeller shaft 54 with the transmission 53 omitted, and to directly connect the motor 52 to the differential gear into one body with the propeller shaft also omitted.
And, it is also known to omit a speed reducer and a transmission mechanism and to incorporate a motor into the right and left wheels to provide a direct drive system to directly drive the right and left wheels by each motor.
Besides, such an electric vehicle generally uses a regeneration brake in addition to a common mechanical brake, differing from the conventional gasoline automobile. The regeneration brake temporarily uses the propelling motor as a generator at the time of reducing the speed of the vehicle when the brake is activated, converts the motion energy to be reduced for decelerating the vehicle into the electric energy by the motor generation, and recovers the obtained electric energy into the storage batteries.
Therefore, as compared with the mechanical brake utilizing a frictional braking force owing to a physical contact, the regeneration brake utilizes a non-contact, electromagnetic braking force, so that degradation of the braking force due to heating at frictional braking and lowering of the performance due to friction can be avoided, and reliability and durability of the braking device are improved. And, by the regeneration brake, the deceleration performance similar to the acceleration performance by the motor can be obtained in principle, and electricity generated by the motor can be controlled by electrically controlling, so that a regeneration braking force can be set and controlled arbitrarily.
However, since a general electric vehicle uses a single propelling motor to distribute the motor-driven force to respective wheels through a mechanical transmission mechanism, it has a disadvantage that a transmission, a propeller shaft and a differential gear which form the transmission mechanism are made large. And, since these rotary parts have a high inertia moment, energy required for acceleration is increased, and the transmission efficiency of the motor-driven force is lowered.
And, since the vehicle space is largely occupied by the above members, there are disadvantages that the vehicle appearance is adversely effected, and flexibility of designing the vehicle body is limited.
Besides, since the direct driving does not have a transmission, the motor's low efficient zone is used depending on a broad traveling speed range of the vehicle, resulting in a disadvantage that the motor efficiency is lowered. Especially, when the vehicle is traveling at a low speed, this tendency is prominent and a high-power motor is needed, so that the motor size becomes large and the total performance is lowered.
Furthermore, the vehicle having a transmission needs to accurately detect a traveling speed of the vehicle to operate the transmission in order to change the speed, and it is general to obtain the traveling speed from the revolving speeds of the propelling wheels. But, since the propelling wheels slip depending on a traveling condition, it is hard to detect the actual traveling speed based on the revolving speeds of the propelling wheels.